1. Field of the Invention
The invention relates to a method of manufacturing a plate of gel for separating and transferring macromolecules by electrophoresis, and also to plates of gel obtained by performing the method.
2. Description of the Prior Art
Such plates comprise a layer of gel, e.g. agarose or polyacrylamide, adhering to one face of a thin microporous membrane, e.g. made of nitrocellulose, "nylon", PVDF (polyvinylidene difluoride), or even special paper. Samples of macromolecules such as nucleic acids or proteins are deposited in wells formed in the layer of gel at one end of the plate, and the plate is then placed in a bath of appropriate liquid between electrodes of opposite polarities. Under the effect of the electric field between the electrodes, the macromolecules move longitudinally through the layer of gel at speeds that are a function of their molecular masses. At the end of a given length of time, they will have travelled lengths or distances that differ as a function of their molecular masses, and they can thus be separated from one another. They are then transferred through the thickness of the gel onto the membrane that adheres to the plate of gel, for the purpose of hybridizing and subsequent detection.
The plates of gel used in this known (so-called "Multi-Blotter") technique for separating and transferring macromolecules must satisfy a certain number of criteria, such as planeness of the membrane, constant thickness of the gel, uniformity of the gel, no bubbles of air in the gel or at the gel-membrane interface, and cleanness of the free face of the membrane opposite from its face covered with gel.
To manufacture such plates, it is possible to fix membranes around their peripheries to frames, and then to cast the gel while in a very liquid state into such frames in order to cover the membranes. The gel is then allowed to set. The gel naturally adheres quite strongly to the membranes and tends to fill the micropores in the membranes by capillarity.
When the membranes are placed on a plane surface for the gel to be cast, plates are obtained having membranes that are plane, but that leave traces of gel or that have gel of thickness that varies to a greater or lesser extent on the faces of the membranes opposite from the faces that are normally covered in gel. During casting, the very liquid gel penetrates into the membranes and passes through them so as to come into contact with the support surface where it accumulates to a greater or lesser extent. In addition, bubbles of air are often held captive between the membrane and the gel or within the gel.
In contrast, if support is provided only for the peripheral frames to which the membranes are fixed while the gel is being cast, then the membranes themselves are no longer supported by a plane surface, so their free faces remain clean, but the membranes become curved under the weight of the gel and take up a bulging shape that they retain once the gel has set.
To avoid those drawbacks, proposals have already been made to saturate the membranes with water before casting the gel and then to place them on a plane surface and to subject them to rolling in order to eliminate bubbles of air and make the membranes adhere to the plane surface. The gel is then cast on the membranes while they are resting on said plane surface. The water present in the micropores of the membranes prevents the gel from passing through the membranes, thereby ensuring that the faces of the membranes opposite to those that are covered with gel remain clean.
Nevertheless, that known method is very lengthy and fiddley to perform, and it does not enable plates of gel to be made quickly.